A flow battery system is a rechargeable fuel cell exploiting the fluid dynamics, kinetics, and chemical potential properties of fluids containing electroactive elements (i.e., electrolytes) to convert chemical energy to electrical energy. The electrolytes typically comprise a catholyte fluid and an anolyte fluid, where each are stored in separate electrolyte tanks. At least one pump for each tank, directs the electrolytes from the electrolyte tanks and into a cell stack (comprising of one or more cells). The electrolytes come into contact with electrodes to generate electrical energy, which is typically stored in current collectors of the cell stack. A power source or load is placed into electrical communication with the cell(s) to selectively draw electrical power from the flow battery system.
Each cell typically comprises a positive electrode disposed on a first side of a membrane and a negative electrode disposed on a second side of a membrane. The membrane facilitates movement of the electroactive elements and the exchange of electric charges. A flow frame substantially encases the electrodes and membrane, and contains the electrolytes as they are directed into, and out from, the cell stack by the pump(s). The flow frame typically comprises two or more members that are configured to compress the cell components together, and are secured together via a fastener, fused together, or otherwise sealed. The flow frame creates a flow compartment within which the cell components are contained, and it is generally provided with inlets and outlets to facilitate fluid communication with a manifold that is in further fluid communication with the tanks.
In systems with multiple cells, a plurality of cells are arranged in electrical series, with each cell being separated by bipolar plates to facilitate passage of electricity while keeping the electrolytes inside. The bipolar plates create flow sub-compartments, such that each flow sub-compartment has opposite polarities and contains an electrode of a respective polarity. Monopolar plates are typically disposed at terminal ends of the stack, and the electrodes, monopolar plates, and bipolar plates are in electrical communication with the current collectors.
Performance of these flow battery systems is directly related to internal resistance, current transfer efficiency, the feed pressure of the pumps, and material degradation of the component parts. The electrolytes should generally exhibit high ionization and chemical kinetics and have a low viscosity. The electrodes generally should exhibit resistance to acid, have a high specific surface area, and be good electrical conductors. The membrane generally should enable ion transfer, but prevent, or at least inhibit, mixing of the electrolytes, and also exhibit consistent diffusion and electrical resistivity properties. The flow frame members generally should exhibit resistance to acid, maintain a steady compressive force upon the electrodes and membrane, and adequately contain the electrolytes as well as the component parts.
Prior art in this field consists of flow battery systems employing sealants and gaskets, such as rubber O-rings, disposed between the flow frame members to prevent leakage of the electrolyte from the cell. Use of separate seals in the flow battery system poses several problems. These seals tend to degrade, leading to a failure to contain electrolytes. The use of separate seals increases the number of parts comprising the flow battery system, which increases the probability of system failures and adds to manufacturing and maintenance costs.
The present invention is directed toward overcoming one or more of the above-identified problems.